Studies to be conducted during this phase of the proposal involve a kinetic evaluation of the role of monovalent metal ions in the activity of activated bovine plasma protein less than (APC). This enzyme exerts its influence through inactivation of Factor Va, a protein which is necessary for production of thrombin. Our evidence suggests that the presence of monovalent cations stimulates the activity of APC and we will evaluate the kinetic properties of this novel function of monovalent cations in blood coagulation. We also will evaluate the properties which a lipid system must possess to enhance the coagulation process. We will study this aspect by preparing and determining the biophysical properties of synthetic lipid vesicles and then examining their effectiveness in specific individual reactions involved in blood clotting. Since many factors affect the lipid compositions of molecules in vivo (e.g., age, detachment, etc.), we can address the question of how alterations in lipids in physiological macromolecules can affect coagulation.